Tamoxifen for the prevention of breast cancer

News p 1187 The complexity of the effects of tamoxifen has recently been summarised: “Tamoxifen is an antioestrogen with complex pharmacology encompassing variable species-, tissue-, cell-, gene-, age- and duration of administration-specific effects, from oestrogen-like agonist actions to complete blockade of oestrogen action. This complexity is consistent with the various, and sometimes paradoxical, effects that have been associated with tamoxifen administration in animals and humans.”1 The report concluded that there was sufficient evidence that tamoxifen increased the risk of endometrial cancer and conclusive evidence that it reduced the risk of contralateral breast cancer. Because of this complexity of effects, a consensus has existed until recently that using tamoxifen for preventing breast cancer was questionable even in clinical trials, and that only trials in women at high risk of breast cancer could be justified.2 This month, however, investigators from the National Cancer Institute-National Surgical Adjuvant Breast and Bowel Project decided to release the initial results of the Breast Cancer Prevention Trial, based on their assessment that a reduction in breast cancer had been shown in the group receiving tamoxifen (p 1187).3 Should we now conclude that the evidence is sufficient to warrant the widespread use of tamoxifen for …